Experimental evidence on RH-dependent crossover from an electronic to protonic conduction with an oscillatory behaviour

An oxide semiconductor changes its resistance with exposure of water molecules and is accepted to be governed by electronic and protonic conduction in low and high humid atmosphere, respectively, without any experimental evidences. Here, we report on the experimental evidence of a relative humidity (RH) dependent crossover, from an electronic to protonic conduction and its oscillatory behaviour in mesoporous SnO2. Interestingly, oscillatory conduction observed in the intermediate humidity range (70%-90% RH) lies in between two monotonic variations that substantiate the competitive adsorption and desorption processes of oxygen species and water molecules. In addition, we have shown that the conduction process can be tuned predominantly electronic or protonic by pre-and post-UV treatment. The conductance increases by 2-3 orders as the conduction changes from pure electronic to protonic, suggesting an insulator-to-metal like transition. Published by AIP Publishing.